Prediction of dynamic characteristics of a dual-rotor system with fixed point rubbing—Theoretical analysis and experimental study

• Fixed point rubbing characteristics of a dual-rotor system are investigated.
• The phenomena of beat vibration are observed in the simulation and experiment.
• The combination frequencies for fixed point rubbing are theoretically and experimentally identified.

For theoretical and experimental research on the fixed point rubbing of aero-engine, a dual-rotor system capable of describing the mechanical vibration resulting from two imbalances and fixed point rubbing is established in this paper. Considering the effects of the softer coatings painted on the discs and casing, the Lankarani–Nikravesh model is applied to describe the impact force between the compressor disc of the low pressure rotor and the casing convex point. Meanwhile, the Coulomb model is used to simulate the frictional characteristics. Then the motion equations of the dual-rotor system with fixed point rubbing are solved by the Runge–Kutta method and the complicated responses at different rotational speeds are analyzed by the 3D waterfall plot, waveform and frequency spectrum. To verify the effectiveness of the dual-rotor system dynamic model, the experiment of fixed point rubbing is performed on a dual-rotor test rig. The vibration displacement of the low pressure rotor is obtained from the data measured in the impact experiment. The numerical results and experimental results indicate that for the dual-rotor system without rub-impact, the phenomena of beat vibration occur at the certain rotational speed ratio. Moreover, for the case of fixed point rubbing, several combination frequencies in the responses of the dual-rotor system are identified as the particular fault frequencies.